Motor-control system.



W. 0. LUM.

MOTOR CONTROL SYSTEM.

APPLICATION FILED APR. 24. 1913. RENEWED was 8. I911.

1,255,447. Patented Feb. 5, 1918.

WITNESSES: INVENTOR I BY v ATTORNEY WALTER 0. LUM, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Patented Feb. 5, 1918.,

Application filed April 24, 1913, Serial No. 763,389. Renewed June 8, 1917. Serial No. 173,647.

To all whom it may concern:

Be it known that I, WALTER O. LUM, a citizen of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Motor-Control Systems, of which the following is a specification.

My invention relates to systems of electric motor control and it has special reference to systems of control in which starting resistors are controlled by sets of automatically operated switches.

My invention has for one of its objects, to provide a system of the above indicated character which will be entirely automatic in its action and which will operate to cut out steps of the starting resistor in a predetermined order.

A further object of my invention is to provide a system of control in which the shunt field of the motor is automatically weakened when the armature resistance has been cut out.

In the operation of motors for driving planers and other machinery requiring frequent stops and reversals, it is highly desirable that a system of control be employed that permits of rapid acceleration. To prevent the loss of time and to avoid the attention required in manual operation of the starting device, it is essential that the system of control be entirely automatic in its operation.

My invention consists of a plurality of successively actuated switches which control the sections of the starting resistor in a motor circuit. Each of the actuating coils of the several switches is connected in the controlled circuit by the operation of the preceding switch. The last switch in the series operates to insert resistance in series with the shunt field winding simultaneously with the short-circuiting of the last step of the armature resistor.

vThe single figure of the accompanying drawing is a diagrammatic view of a system of electric motor control arranged in accordance with my invention.

Referring to the drawing, an electric motor 1 is supplied with electrical energy from any suitable source, through line conductors 2 and 3. The motor 1 comprises an armature 4 and a shunt field winding 5 and is provided with a starting resistor 6 and a series.

field resistor 7 that is in series with the shunt field winding 5. The starting resistor is divided, by intermediate connections, into steps or sections 8, 9 and 10 which are controlled by a series of magnetically actuated switches 11, 12 and 13. The switches 11, 12 and 13 are provided with movable core members 14, 15 and 16 which actuate switch members 17, 18 and 19 to bridge contact member 20, 21 and 22.

The switch 11 is constructed on the lockout principle, whereby an excessive current prevents its closure. The switch 11 comprises a series coil 23 and a casing 24 that is provided with a pole piece 25 at one end. A tubular member 26 is adjustably connected to the casing 24 at its opposite end. The movable core member 14: is provided with an enlarged head 27 and a stem 28 which occupies an opening 29 in the tubular mem ber 26. When the series coil 23 is energized byan excessive current, the stem 28 becomes saturated magnetically, and afiux is produced across the small air gap between the head 27 and the upper end of the member 26. The head 27 is held in its lower position by the resultant magnetic attraction. The air gap between the head 27 and the pole pieces 25 is a part of the magnetic circuit and there is, consequently, a magnetic attraction between these two members while the coil 23 is energized. When the current becomes normal, flux ceases across the first mentioned air gap and the core member 25 is drawn upwardly to cause the switch member 17 to bridge the contact members 20.

The switches 12 and 13 are provided with actuating coils 30 and 31 that are respectively in series with the contact members of the preceding switch. The switches 12 and 13 are also provided with holding .coils 32 and 33 that are in series with the contact members of the same switch and the actuating coil of the succeeding switch in the The holding coils have a greater number of turns than the actuating coils in order that a smaller current may operate to hold the switches closed.

.A shunt circuit for the field .resistor 7 is controlled by a relay 34 of the well known fluttering type which comprises a series coil 35 and a movable core member 36 that is connected to a switch member 37. Contact members 38 are connected in the shunt circuit and are bridged by the switch member 37 when the core member 36 is drawn upwardly. The holding coil 33 of the switch 13 is connected to the coil 35 at an intermediate point in the latter. The connection is made at a point which so divides the coil into two parts 39 and 40 that, when the part 39 is short circuited by the preceding switch 13, the remaining part 40 has an insufiicient number of turns to hold the switch member 37 closed when the current traversing it does not exceed a normal value. When the current exceeds a predetermined value, the switch member 37 is closed to shunt the resistor 7.

V7 hen it is desired to start the motor, the main switch 41 is closed and electrical energy is supplied to the motor. The motor circuit extends from the line conductor 3 through the switch 41, coil 35, resistor 6, coil 23, armature 4, conductor 42, and the switch 40 to the line conductor 2. The coil 35 operates immediately to draw the core 36 and the switch member 38 upwardly to close the shunt circuit around the field resistor 7. W hen the current has fallen to a value determined by the adjustment of the switch 11, the coil 23 draws the core 14 upwardly, and the switch member 17 bridges the contact members 20. Current then flows from the point of connection between the sections 8 and 9 of the resistor 6 through the coil 30, across the contact members 20 to the coil 23, and section 8 is thereby short-circuited. The actuating coil 30 is energized by the connections just described to draw the core 15 and the switch member 18 upwardly to bridge the contact member 21 and thereby connect the holding coil 32 in circuit with the actuating coil 31. The resistor sections 8 and 9 and the coils 23 and 30 are short-circuited by the above connections but the switch member 18 is held closed by the holding coil 32. The switch member 19 is operated in alike manner to short-circuit the resistor section 10 and the coils 31 and 32, the holding coil 33 retaining the member 19 in its closed position. The closing of the member 19 short-circuits the part 39 of the coil 35, allowing the core 36 to dro and thereby cause the switch member 3 'to open the shunt circuit for the resistor 7. The resultant weakening of the motor field causes a rush of current in the motor circuit which comprises the part 10 of the coil 35. If the current exceeds a predetermined value, the part 40 is sufficiently energized to draw the switch member 37 upwardly to again complete the shunt circuit for the resistor 7. When the armature current fall below the predetermined value, the switch member 37 opens the shunt circuit for the resistor 7. This oscillating action continues until the motor speed has reached a value at which the armature current does not exceed the predetermined value, whereupon the switch member 37 remains in its open position. This construction insures that the motor cannot be accelerated by weakening its field before the resistance of the armature circuit has been entirely out out and that this acceleration will take place immediately upon that condition having been reached. By means of the holding coils, the switches are held closed until the succeeding switch has been closed.

It will be understood that many changes may occur to one skilled in the art. Such modifications may be made as fall within the scope of the appended claims.

I claim as my invention:

' 1., The combination with an electric motor, a starting resistor therefor, and a plurality of switches for controlling said resistor, of a field resistor, a relay for controlling said field resistor, said relay com prising a coil and means for electrically connecting one of said switches to an intermediate point of said coil.

2. The combination with an electric motor, a starting resistor therefor, and a plurality of switches for controlling said resistor, of a field resistor, a relay for C011",

trolling said field resistor, said relay comprising a coil, and means for electrically connecting one of said switches to an intermediate point oi said coil whereby a portion of said coil is shunted upon the closing of said switch.

3. The combination with an electric motor, a field resistor therefor, a relay switch for controlling said resistor, said switch having a coil, which operates to maintain the closure of said switch when the armature current exceeds a predetermined value, of means for automatically varying said we determined value.

4. The combination with an electric motor, a starting resistor therefor and means for shunting said resistor, of a field resistor for said motor, a relay switch for controlling said field resistor, said switch having a coil which operates to maintain the closure of said relay switch when the armature current exceeds. a predetermined value, and means for varying aid predetermined value when said starting resistor is shunted.

5. The combination with an electric motor, a starting resistor therefor and means for shunting said resistor, of a field resistor for said motor, a relay switch for controlling said field resistor, said switch having a coil which operates to maintain the closure of said relay switch when the armature current exceeds a predetermined value, and means for increasing said predetermined value whensaid starting resistor is shunted.

6. The combination with a motor, of a starting resistor, a series of successively-acmeans whereby the actuation of the last in order of said switches operates said field relay, said means comprising means for short-circuiting one part of said coil.

7. The combination with a motor, of a starting resistor therefor, a series of progressively-operated switches for controlling said resistor, a field relay comprising an actuating coil, and means whereby the closure of the last in order of said switches operates to short-circuit a portion only of said coil.

8. The combination with a' motor, of a starting resistor therefor, a shunt circuit for said resistor, a field resistor, a shunt circuit for said field resistor, and means for breaking the shunt circuit for said field resistor simultaneously with the completion of the shunt circuit for said starting resistor, said means comprising a switch having a coil that is divided into two parts by an intermediate connection and means for shunting one of said parts.

9. The combination with a motor of a starting resistor therefor, a series 0% progressively-operated switches for controlling said resistor, a field relay comprising an actuating coil, and means for electrically connecting the last in order of said switches to an intermediate point of said actuating coil.

10. The comb nation with a motor, of a starting resistor, a shunt circuit for said resistor, a field resistor, a switch for controlling said field resistor, said switch comprising an actuating coil connected in series with said starting resistor, s'aid coil having a portion common to said series connection and said shunt circuit.

11. Thecombination with a motor, of a starting resistor therefor, a series of successively-actuated switches for controlling said resistor, and means whereby the last switch in order of said series automatically controls the field excitationof said motor, said means comprising a field resistor, a

relay switch for controlling said field resistor, said relay switch having a coil and means for electrically connecting said last switch to an intermediate point of said coil.

12. A motor controller rovided with a. field controllin relay sensitive to predetermined variations in the armature current, and means for increasing the sensitiveness of said relay for a temporary period in starting.

'13. A motor controller provided with a field controlling relay sensitive to variations in the armature circuit for varying the field strength of the motor and automatic controlling means for said relay rendering the same sensitive to certain current variations during starting and to other current variations thereafter whereby field weakening isprecluded in starting.

14. A motor controller provided with a field controlling relay having a plurality of cumulative windings sensitive to the armature current in starting and means automatically excluding one of said windings from circuit after a temporary period.

In testimony whereof, I have hereunto subscribed my name this 16th day of April, v

WALTER O. LUM.

Witnesses:

J. H. ALBRECHT, B. B. HINEs. 

